The present invention relates to a zoom lens used in an image pickup device and the like and particularly to an interchangeable wide angle zoom lens used in a digital single lens camera and the like.
As for the wide angle zoom lens of digital camera, an optical system having a long back focus is required in order to provide a space into which optical elements such as filters are inserted right in front of an electronic image pickup plane while securing a wide angle of view. As such an optical system, a retro-focus type optical system is widely applied that has a front group of negative refractive power and a rear group of positive refractive power. If a so-called oblique light incidence situation occurs in which an incident optical beam tilts with respect to an optical axis when striking the electronic image pickup plane after passing through the optical system, the amount of peripheral light decreases, and shading and color drift occur. Therefore, an optical system has been proposed to maintain telecentricity of the incident optical beam. Such a type of technology is disclosed in JP-A-4-217219, JP-A-6-94996, JP-A-11-52246, or JP-A-2005-37727.
In recent years, a compact wide angle zoom lens of digital camera is required whose overall length of the lens is made shorter with a high variable magnification ratio. If an optical system has fewer lenses to achieve downsizing, it is difficult to design the optical system that maintains telecentricity while securing a wide angle and suppressing various types of aberration. However, in recent years, technologies have been proposed to correct distortion to some extent by using electric signals as the technologies of electronic image pickup elements advance. Therefore, it is not necessary to pay particular attention to distortion correction in correcting aberration.